Electrical apparatus



June 22, 1948..

E. F. M NlcHoL, JR 2,443,794

ELECTRICAL APPARATUS Filed Feb. 19, 194

| I I l I I i ee l I I I I [GENE/PA TOR| I INVENTOR. F JEDW4RD FMAcN/CHOL JR.

Patented June 22, 1948 Edward F. MacNichol, Jr., Wenham, Mass., as-

signor, by mesne assignments, to the United States of America asrepresented by the Scoretary of War Application February 19, 1945,Serial No. 578,766 8 Claims. (01. 315-370) This invention relates toelectrical apparatus, and particularly to means for determining certaincharacteristics of electron tubes.

Expandinguses of electron tubes above and beyond the types of operationknownin the prior art have madenecessary other types of tests of theseelectron tubes than those .known and used heretofore, and other meansfor making these tests, so that the operational and dependabilitycharacteristics of the electron tubes may be determined under these newconditions of use. Uses now made of electron tubes, such as in pulsegen.-

.erators, pulse amplifiers and other associated work require theprovision of tube performance data or characteristics which would not beavailable ordinarily. The required characteristics'in the type of workcontemplated by the present invention include the ratio variouselectrodes. i i

In accordance with the present invention there is provided apparatus fordetermining the characteristics of an electron tube under conditions ofpulsed operation. The electron tube under test must have at least afirst, second and third electrode. The apparatus comprises a source ofpower connected to the electrodes of the electron tube and a pulsesource. A coupling means is used for feeding the pulses from the pulsesource to. the first electrode of the electron tube. The pparatus alsoincludes an indicating means which is connected to the circuit of. thefirst electrode and one of the other remaining elec: trodes of theelectron tube. The circuit of the first electrode includes a resistorand the circuit of said one of the other electrodes includes apotentiometer. The-potentiometer is adapted to indicate the ratio of thecurrent in the potentiometer to the current in the resistor when a pulseis fed to the first electrode and the indicating means shows theresistances in the efiective part of the potentiometer and in theresistor are properly proportioned.

Hence, an object of this invention is to provide means for expeditiouslydetermining the required of the currents in the tube characteristics.

' Other objects of the invention will be apparent from the followingdescription and the appended claims, taken in connection with theaccompany ingdrawings,in which: '1 Fig. 1 shows a. schematic diagram ofone em- 2 bodiment of electrical apparatus which may be used fordetermining characteristics of electron tubes;

Fig. 2 shows a schematic wiring diagram of an--;. other embodiment ofelectrical apparatus which may be used for determining characteristicsof electron tubes; and,

Fig. 3 is a fragmentary schematic diagram of a circuit which is adaptedfor combining the features of the apparatus illustrated in Figs. 1 and2..

Referring now more particularly to Fig. 1 of the drawings, there isshown in this embodiment.

of the invention a circuit for determining the ratio of the platecurrent to the grid current of an electron tube. The circuit, as shown,includes.

a pulse source I I preferably a pulse generator and a coupling means I2preferably a pulse transformer. The couplin means I2 is adapted tocouple the pulse source i I to a grid ll of an electron .tube l3'so thatthe pulse to the grid I1 will be a positive going pulse. The tube i3 isthe tube being tested and may be any electron tube :with at least threeelectrodes. However, in the illustrations in Figs. 1, 2, and 3 the tubeis a triode.

A grid load resistor I4 is connected as shown be tween the transformerl2 and a source of negative bias sufficient to maintain the tube I 3jatthe desired operating point, normally at cutofli A potentiometerconsisting of a plate load resistor l5 and a variable tap I6, isconnected between an anode ll; of the tube l3 and a source of positivevoltage which is normally between +300 and +1000 volts. The resistor I 5is equal in magnitude to the resistor I4. i The potentiometer I5-l 6 maybe calibrated in a manner hereinafter described so that from thecalibration the characteristicsof tube l3 may be read directly. Acathode IQ of the tube I3 is connected toground as shown. An indicatingdevice 2| such as a cathode ray oscilloscope, peak readingvoltmeterorother peak reading device is includedin this circuit to show therelative amplitudes of voltages developed across the grid resistor l4and across the effective portion of the potentiometer Iii-l6. One sideof the indicating device is connected to the potentiometer l5'|6 througha coupling ca pacitor 22 and the other side is connected throughafcoupling capacitor 23 to a point between the secondary of transformerl2f and the'resistor I 4. The rest of the connections of the indicatin 3meansare not shown but are connected in any suitable manner well knownin the prior art.

A pulse is applied to the tube 13 from the pulse generator I! throughthe. pulse transformer 2. The current ig which flows in the grid circuitwill produce a variational voltage at 24 of the form shown at 24 in Fig.l and is equal to:

where V24 is voltage at 24 relative to bias is is grid current R14 isresistance of resistor I 4 When the grid is driven positively abovecutoff.

plate current in will flow causing a Variationalvoltage to appear at 25of the form shown at 2.5 in Fig. l and is equal to:

Where V25 is voltage at 25 relative to plate battery ip is plate currentr is the resistance of resistor I5 from tap [6 to Also referred to asthe efiective resistance of potentiometer li5-l 6.

It is assumed that grid bias is su'fficient to eliminate both grid andplate current except during the pulses; if this is not the case only thechanges in current and voltage should be used. This might .be otherwiseexpressed in terms of pulse voltages since only the variations can passthe blocking condensers to the oscilloscope. The tap [B is adjusted sothat the peak voltage value V25 is equal to peak voltage value V24. Thisequality is indicated by no deflection on the oscilloscope 2.1 whenconnected .as shown in Fig. 1. We then have that: (3.) V124=V25 From theabove three equations we .get:

5, plate cur-rent -"i r grid current However, since resistor 44 is equalin magnitude toiliesistor r-| fiithen The tapped resistor 1.5 may nowbe'calibr-ated .to

the cathode :current to the .-.grid- :current of an electron tube. Thecircuitsas shown, includes a pulse source 31 #preferably arpulsegenerator :3! and arcoupling' means32 preferably'a pulse transformer:connected "to transfer pulses from the pulse generator 134 .toa grid3411f anelectrontube 33. The i-pulse at the grid iJLncrmally isaposttive goin-g ;pulse. n grid load resistor .34 is .connected rasshown between the coupling :-means .32 and .asource .of negative .bias.The inegative bias appliedto thesgrid 3.1 through.the..resistor,34 .has

a value whichiis :suitable .to maintain the tube .33

normallyat .cutofi. Theconnection'ofrthe resistor 34 permits the currentflowing in the circuit of the grid 31 to develop a voltage across thisresistor 34. A potentiometer consisting of a cathode load resistor 35and a variable tap 3B is connected between a cathode 38 of the tube 33and ground. The resistor 35 is equal in magnitude to the resistor 34. Ananode 39 of the tube 33 normally is connected directly to a source ofpositive voltage as shown. The same conditions of biasing will normallybe used in the circuit in Fig. 2 as are used in the circuit in Fig. 1.An indicating device 4| such as an oscilloscope, peak reading voltmeteror other peak indicating device is included in the circuit in Fig. 2 toshow the relative amplitudes ef-voltages developed across the gridresistor 34 I and across the effective portion of the potentiometer'35--36. The indicating device is connected to the potentiometer 35-36and to a point between the resistor 34 and the secondary of thetransiormer 82 as shown in Fig. 2. The rest of the connections of theindicating means 4| are not shownbut are made in a suitable manner wellknown in the prior art. As will be noticed, the connections of theindicator 2| in Fig. 1 are different from the connections of theindicator 4! in Fig. .2. The reason for this is because of the oppositepolarities of the two voltages being come pared in'Fig. 2.

A pulse is applied to the tube 33 from pulse generator 3| through thepulse transformer 32. The current i which flows in the grid circuit willproduce a variational voltage at 42 of the form shown at 42 in Fig. 2and is equal to:

(7) Vaz i Rai where V4215 voltage at 42 relative to bias z is gridcurrent R34 is resistance of resistor 34 When the grid .31 is drivenpositively above cutofi, cathode current i1: will flow causing aVariational voltage to appear at 43 of the form shown at 43 in Fig. 2and equal to:

where The tap 36 is adjusted so that the peak voltage value VA3 is equalto the peak voltage value Va. This equality 'isindicated on theoscilloscope 4! of Fig. 2. We then have:

('95) tVaz Vaa and solving the .above' three equations we ohtainz,

i ii cathode current a z rid current However, since resistor .34 isequal in magnitude toresistorBEthen:

'2 T The tapped resistor 35 may now be calibrated to read the ratio.Raa/r and the reading when the two aforementioned voltages are equalwill be the desired characteristic under the ,biasing con-d1 tions used.From Equation IQ-itmaybeseemthat if resistor .35 is calibrated to .readthe. iresistance ofthe resistor-'34 divided by r(R,s4/r) then resistor35 need not equal resistor 34 in magnitude.

(12) reading=ratio E Fig. 3, as hereinbefore stated, illustrates onemeans of combining the-features of the circuits illustrated in Fig. 1and Fig. 2. By means of a switch 5|, there may be inserted in the platecircuit of a tube 52 either a resistor 53 or a shunt 54. By means of aswitch 55, mechanically connected to switch 51, there may be inserted inthe cathode circuit of tube 52 either a shunt 56 or a resistor 53. Bymeans of switch-59 alsomechanicallyconnected to switch 5i theappropriate connections aremade to oscillograph 6! as in Figures 1 and2. It will be observed that placing the resistor 53 in the'plate circuitplaces the shunt in the cathode circuit and vice versa. The grid of tube52 is connected through grid resistor 64 and coupling transformer 62 fedby pulse generator 63, with a terminal 65 corresponding to terminals 34and 42 in Figs. 1 and 2. The tap 57 on resistor 53 is connected to anindicating device. If the indicating device is an oscilloscope, then thetap 5'! is connected to the oscilloscope through switch 59 as in Figs. 1and 2. With the tube 52 connected in the manner just described it ispossible to measure with one system both the ratio of cathode current tothe grid current and the ratio of anode current to the grid current.

While there has been described what is at present considered thepreferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

I claim:

1. An' apparatus for determining the characteristics of an electron tubeunder conditions of pulsed operation, said tube including at least acathode, a grid, and an anode, said apparatus comprising a power supplyhaving at least a positive terminal, a negative terminal, and anintermediate terminal; a pulse source; a pulse transformer for couplingsaid pulse source to said grid; a grid load resistor connected in serieswith said negative terminal, said pulse transformer and said grid; atsecond load resistor, equal in magnitude to said grid load resistor andhaving a variable tap, said second load resistor being calibrated togive the ratio of the resistance of said second load resistor to theresistance of said second load resistor from said tap to one end of saidresistor; means for switching said load resistor selectively betweensaid anode and said positive terminal with said end of said loadresistor connected to said positive terminal and between the cathode andsaid intermediate terminal with said end of said load resistor connectedto said intermediate terminal; means operative with said switching meansto close the electrode circuit into which said second load resistor isnot connected; and means for comparing the voltage developed across saidgrid load resistor by the current flowing through said grid loadresistor, with the voltage developed across the portion of said secondload resistor from said tap to said end by the current flowing throughsaid second load resistor, said tap being adjustable to cause said twovoltages to be possible of equalization in magnitude so that the ratioof current through said second load resistor;

to the current through said grid load resistor may be read from thecalibration of said load resistor. r i i q 1' a 2. An apparatus fordetermining the characteristics of an electron tube under conditions: ofpulsed operation said tube including at least; a first, second, andthird electrode, said apparatus comprising a power supply having atleast a positive terminal, a negative terminal, and an. intermediateterminal; a pulse source; a pulse transformer for coupling said pulsesource tosaid second electrode; a first load resistor connected inseries with said negative terminal, said pulse transformer and saidsecond electrode; a second load resistor having a variable tap,saidsecond load resistor being calibrated to give the ratio of theresistance of said first load resistor to the resistance of said secondload resistor from said tap to one end thereof; means for switching saidsecond load resistor selectively, between said third electrode and saidpositive terminahwith said end of said second load resistor connected tosaid positive terminaLand between said first electrode and saidintermediate terminaLowith said end connected tosaid intermediateterminal; shunt means operative with said switching. means to close theelectrode circuit into which said second load resistor is not connected;and means for comparing the voltage developed across said first loadresistor by the current flowing through said first load resistor, withthe voltage developed across the portion of said second load resistorfrom said tap to said end by the current flowing through said resistor,said tap being adjustable to make possible equalization of the two saidvoltages so that the ratio of the current flowing in said second loadresistor to the current flowing in said first load resistor may be readfrom thecalibration of said secondload resistor.

3. An apparatus for determining the characteristics of an electron tubeunder conditions of pulsed operation, said tube including at least acathode, a grid, and an anode, said apparatus comprising a power supply.having at least a positive terminal, a negative terminal, and anintermediate terminal; a pulse source; means for coupling said pulsesource to said grid; a grid load resistor connected in series with saidnegative terminal, said coupling means, and said grid; a plate loadresistor connected between said anode and said positive terminal, equalin magnitude to said grid load resistor, and having a variable tap, saidplate load resistor being calibrated to give the ratio of the resistanceof said plate load resistor to the resistance of said plate loadresistor from said tap to said positive terminal; and means associatedwith said grid load resistor and said tap for comparing the voltagedeveloped across said grid load resistor by current flowing through saidgrid load resistor, with the voltage developed across that por tion ofsaid plate load resistor from said tap to said positive terminal bycurrent flowing through said plate load resistor, said tap beingadjustable to make possible equalization of the two said voltages sothat the ratio of the current flowing in said plate load resistor to thecurrent flowing in said grid load resistor may be read from thecalibration of said plate load resistor.

4. An apparatus for determining the characteristics of an electron tubeunder conditions of pulsed operation, said tube including at leastcathode, grid, and plate elements, said apparatus if 2 comprising-apower supply having at least a positive terminal, a negative terminal,and an intermediate terminal; a pulse source; means for coupling saidpulse source to said grid; a grid load resistor connected in series withsaid negative terminal, said coupling means and said grid; a cathodeload resistor, equal in magnitude to said grid load resistor andconnected between said cathode and said intermediate terminal and havinga Variable tap, said cathode load resistor being calibrated to give theratio of the resistance of said cathode load resistor to the resistanceof said cathode load resistor from said tap to said intermediateterminal; and means associated with said grid load resistor and said tapfor comparing the voltage developed across said grid load resistor bycurrent flowing through said grid load resistor, with the voltagedeveloped across that portion of said cathode load resistor from saidtap to said intermediate terminal by current flowing through saidcathode load resistor, said tap being adjustable to make possibleequalization of the two said voltages so that the ratio of the currentflowing in said cathode load resistor to 'the current flowing in saidgrid load resistor may be read from the calibration of said cathode loadresistor.

5. Apparatus for determining the characteristics of an electron tubeunder conditions of pulsed operation, said electron tube including atleast a first, second and third electrode, said ap paratus comprising asource of power connected to the electrodes of the electron tube; apulse source; means for coupling said pulse source to said firstelectrode of the electron tube; indicating means; means for connectingsaid first electrode to said indicating means, said connecting meansincluding a first resistor; potentiometer means connected to saidindicating means; and switching means associated with said potentiometermeans for connecting said potentiometer in series circuit with one ofsaid remaining electrodes and closing a circuit to the remaining of saidelectrodes, said potentiometer being adapted to indicate the ratio ofthe current in said potentiometer to the current in said resistor when apulse is fed to said first electrode and said indicating means showingthat the resistances in the effective part of said potentiometer and insaid resistor are properly proportioned.

6. Apparatus for determining the characteristics of an electron tubeunder conditions of pulsed operation, said electron tube including atleast a first, second, and third electrode, said apparatus comprising asource of power connected to the electrodes of the electron tube; apulse source; means for coupling said pulse source to said firstelectrode of the electron tube; indicating means; means for connectingsaid first electrode to said indicating means, said connecting meansincluding a resistor; and means for connecting said second electrode tosaid indicating means, said second connecting means including apotentiometer, said potentiometer being adapted to indicate the ratio ofthe current in said potentiometer to the current in said resistor when apulse is fed to said first electrode and said indicating means showsthat the resistances in the effective part of said poentiometer and insaid resistor are properly proportioned.

'7. Apparatus for determining the characteristics of an electron tubeunder conditions of pulsed operation, said electron tube including atleast a first, second, and third electrode, said apparatus comprising asource of power connected to the electrodes of the electron tube; apulse source; a pulse transformer for coupling said pulse source to saidfirst electrode of the electron tube; indicating means; means forconnecting said first electrode to said indicating means, saidconnecting means including a first resistor; and means for connectingone of the other of said electrodes to said indicatin means, said secondconnecting means including a potentiometer, said potentiometer beingadapted to indicate the ratio of the current in said potentiometer tothe current in said resistor when a pulse is fed to said first electrodeand said indicating means shows that the resistances in the effectivepart of said potentiometer and in said resistor are properlyproportioned,

8, Apparatus for determining the characteristics of an electron tubeunder conditions of pulsed operation, said electron tube including atleast a first, second, and third electrode, said apparatus comprising asource of power connected to the electrodes of the electron tube; apulse source; means for coupling said pulse source to said firstelectrode of the electron tube; indicating means; means for connectingsaid first electrode to said indicating means, said connecting meansincluding a resistor; and means for connecting one of the other of saidelectrodes to said indicating means, said second connecting meansincluding a potentiometer, said potentiometer being adapted to indicatethe ratio of the current in said potentiometer to the current in saidresistor when a pulse is fed to said first electrode and said indicatingmeans shows that the resistances in the efiective part of saidpotentiometer and in said resistor are properly proportioned.

EDWARD F. MACNICHOL, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,831,744 Laurent Nov. 10, 19312,213,099 Adorjan Aug. 27, 1940 FORMGN PA'I'ENTS Number Country Date753,659 France Oct. 21, 1933

